Lithium-Ion Batteries Overheated in Mitsubishi Vehicles

In yet another setback for lithium-ion battery technology, Mitsubishi Motors has acknowledged that it recently had a fire and an overheating incident involving the high-energy batteries.

The automaker reported early Wednesday that a lithium-ion battery pack intended for the Mitsubishi i-MiEV caught fire while connected to a charge/discharge testing station at a Mitsubishi plant in Okayama Prefecture. In a separate incident, a charged lithium-ion battery installed in an Outlander plug-in hybrid overheated, melting battery cells and part of the battery pack.

”A single one of the 80 cells within the battery pack was overheated, melting adjacent cells,” a Mitsubishi spokesman told Design News in an email. “The 80 cells within the battery pack are divided and set into ‘three blocks’ within the drive battery pack. Examination found that only one of the three blocks sustained any damage.”

Mitsubishi’s Outlander PHEV employs a 12 kWh battery with 80 lithium-ion cells. An Outlander PHEV designed for the Japanese market had an overheating incident that melted cells and part of the battery pack. (Source: Mitsubishi Motors)

Batteries for both of the vehicles were manufactured by a joint venture involving Mitsubishi and GS Yuasa Corp., the company that made the batteries now being used in the Boeing 787 Dreamliner. GS Yuasa did not respond to calls or emails from Design News.

”It’s not clear if there are problems with the batteries from GS Yuasa,” Cosmin Laslau, an industry analyst for Lux Research Inc., told Design News. “But if they contain impurities or contaminants, that would be an issue.”

The lithium-ion batteries used in the Mitsubishi Outlander, as well as the company’s i-MiEV electric car, are believed to use a different chemistry than those employed in the Boeing 787. Both vehicles are said to employ a lithium oxide manganese spinel (LMO) chemistry, whereas Boeing’s units use a more energetic lithium cobalt oxide (LCO) chemistry.

Laslau told us that automakers typically use one of three different lithium-ion chemistries: lithium-iron phosphate (LFP), nickel manganese cobalt (NMC), and LMO. No automakers currently use the chemistry employed by Boeing. ”The auto industry is trying to decide between those three, and determine how they might mix them in a way that combines the best attributes,” Laslau said.

Battery experts have repeatedly warned about the energetic nature of lithium-ion in the past. “In a lithium-ion battery, you’ve got electrodes that are tens of microns from one another,” Elton Cairns, a professor of chemical and biological engineering at the University of California Berkeley, told Design News in 2011. “If you deform the cell case and it causes the electrodes to touch one another, there’s an internal short circuit. That can cause the cell to rapidly discharge and, in so doing, heat up.”

Material scientists said they are concerned about the repeated overheating episodes. “Remember, Li-ion technology is 20 years old now,” Donald Sadoway, John F. Elliott professor of Materials Chemistry at MIT, wrote in an email to Design News. “Shouldn’t we have worked out the bugs by now?”

Laslau said he expects automakers and other users to optimize their lithium-ion chemistries to create a better combination of energy, reliability, cost, and safety. “They might end up being more costly; they might weigh a little more, or they might be a little bit bigger,” he told us. “But these incidents can’t just keep happening.”

I think that engineers have repeatedly underestimated the dangers of lithium-ion, Gorksi. Fifteen years ago, I interviewed Donald Sadoway of MIT and he predicted (in 1998) that engineers would need to be very, very careful with this chemistry, or it would cause problems. It now appears he was right.

It seems that everyone is having problems with these batteries at the same time. If this is new technology why wasn't it tested more rigourusly in the lab and test beds? Is this a case where sales said 'We have to be first and damn the torpedoes of failure."

It seems that everyone is having problems with these batteries at the same time. If this is new technology why wasn't it tested more rigourusly in the lab and test beds? Is this a case where sales said 'We have to be first and damn the torpedoes of failure."

That is a terrible story, tekochip, and I'm sorry for the loss of your friend. This illustrates why it's so important to make these technologies safe before putting them out there on the market. I actually think sometimes these type of electric systems in new cars can do more harm than good especially in situations of a malfunction in which someone wants to get out of a car, which your story very sadly shows.

What a terrible incident. Yes, it's one more reason why potential car fires should never be overlooked. But it also says something about the non-intuitive nature of some of the systems on board today's vehicles. If the doorlock system had been more intuitive, your friend would almost certainly still be alive today.

Car fires should never be overlooked. A number of years ago a good friend of mine died in a car fire. Bob had borrowed a car and was unfamiliar with the electric door locks which locked as soon as the vehicle was put in drive. Pulling on the door latch would not unlock the door, you had to pull the lock pin or use the door switch, then pull on the latch. The power steering pump on the car seized and started a fire that quickly filled the interior with smoke. The autopsy said Bob died in less than thirty seconds from the toxic fumes, and witnesses said that he was pounding on the windows trying to get out.

Thanks so much for that description of the thermal runway, Phil. I understand the issue so much better now. It's interesting to consider the root of the problem and the ways the industry is working to counteract that.

Yikes, I didn't know those statistics about car fires, dbg. It is a bit scary. And yes, battery designs can be made safe, but it seems like some of them haven't quite gotten there yet. I'm sure they will.

A few weeks ago, Ford Motor Co. quietly announced that it was rolling out a new wrinkle to the powerful safety feature called stability control, adding even more lifesaving potential to a technology that has already been very successful.

It won't be too much longer and hardware design, as we used to know it, will be remembered alongside the slide rule and the Karnaugh map. You will need to move beyond those familiar bits and bytes into the new world of software centric design.

People who want to take advantage of solar energy in their homes no longer need to install a bolt-on solar-panel system atop their houses -- they can integrate solar-energy-harvesting shingles directing into an existing or new roof instead.

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